Lock-free sharing of live-recorded circular buffer resources

ABSTRACT

Novel techniques are described for lock-free sharing of a circular buffer. Embodiments can provide shared, lock-free, constant-bitrate access by multiple consumer systems to a live stream of audiovisual information being recorded to a circular buffer by a producer. For example, when a producer system writes a data stream to the circular buffer, the producer system records shared metadata. When a consumer system desires to begin reading from the shared buffer at a particular time, the shared metadata is used to compute a predicted write pointer location and corresponding dirty region around the write pointer at the desired read time. A read pointer of the consumer system can be set to avoid the dirty region, thereby permitting read access to a stable region of the circular buffer without relying on a buffer lock.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to India Provisional ApplicationNo. 201941041686, filed Oct. 15, 2019, entitled “LOCK-FREE SHARING OFLIVE-RECORDED CIRCULAR BUFFER RESOURCES.” The entire contents of IndiaProvisional Application No. 201941041686 is incorporated herein byreference for all purposes.

FIELD

This invention relates generally to memory systems, and, moreparticularly, to lock-free read sharing of live-recorded circular bufferresources.

BACKGROUND

In various types of systems, it is desired to obtain and store audioand/or video data, and to allow other systems to read the stored data asnew data is being obtained. For example, in context of a securitycamera, it can be desirable for the security camera to continuouslyrecord audiovisual information, even while allowing other systems toread the recorded data. Some such systems use circular buffers. Circularbuffers effectively have no beginning or end, so that earlier-recordeddata can continuously and sequentially be overwritten by newly recordeddata (e.g., the newest data continuously overwrites the oldest data inthe buffer). As such, circular buffers can enable continuous recordingwith limited storage capacity.

However, problems can arise when providing read access during suchcontinuous recording, particular when providing read access concurrentlyto multiple systems. Conventionally, when a particular system desires toread from the circular buffer, the particular system requests a bufferlock. For example, the buffer lock halts any new writing to the bufferrestricts all reading only to the particular system to help ensure thatthe particular system can read from a stable environment. While this canbe an effective approach in some cases for a single reading system (andeven, in some cases, for a small number of reading systems), theapproach can have limitations, including not scaling well to largernumbers of reading systems. For example, during the time each readingsystem locks the buffer, new data is not being recorded. As the numberof reading systems increases, the amount of time the buffer is lockedsimilarly increases. At some point, the multiple buffer locks cause nonew writing to occur for an undesirably long period of time. Similarly,at times, a reading system may fail to release its buffer lock (e.g.,though it has completed reading, it fails to unlock the buffer). In suchcases, the entire system can effectively fail, as no new data is writtento the system.

BRIEF SUMMARY

Among other things, embodiments provide novel systems and methods forlock-free sharing of a circular buffer. For example, embodiments canprovide shared, lock-free, constant-bitrate access by multiple consumersystems to a live stream of audiovisual information being recorded to acircular buffer by a producer. Each consumer or producer system cancontinue to access the shared circular buffer resources without waitingfor others of the systems to free the shared circular buffer resources.According to embodiments herein, when a producer system writes a datastream to the circular buffer, the producer system records sharedmetadata. When a consumer system desires to begin reading from theshared buffer at a particular time, the shared metadata is used tocompute a predicted write pointer location and corresponding dirtyregion around the write pointer at the desired read time. A read pointerof the consumer system can be set to avoid the dirty region, therebypermitting read access to a stable region of the circular buffer withoutrelying on a buffer lock.

According to one set of embodiments, a method is provided for lock-freesharing of a circular buffer. The method includes: receiving, at aconsumer system at a request time, a request to read data from acircular buffer having a data stream being written thereto by a producersystem at a bitrate; consulting shared metadata indicating a start timeof the data stream; computing a predicted write pointer locationcorresponding to the request time as a function of the start time andthe bitrate of the data stream; computing a dirty region around thewrite pointer location, the dirty region beginning at a dirty regionstart bit of the circular buffer prior to the write pointer and endingat a dirty region end bit of the circular buffer subsequent to the writepointer; setting a read pointer location for the consumer system as alocation in the circular buffer outside the dirty region; and initiatingreading of data of the data stream at the read pointer location by theconsumer system, the initiating being responsive to the request.

According to another set of embodiments, a lock-free circular buffersharing system is provided. The system includes a write pointerprocessor, a dirty region processor, and a read module. The writepointer processor is to consult shared metadata indicating a start timeof a data stream being written to a circular buffer by a producer systemat a bitrate, and to compute a write pointer location as a function ofthe start time and the bitrate of the data stream. The dirty regionprocessor is coupled with the write pointer processor to compute a dirtyregion around the write pointer location, the dirty region beginning ata dirty region start bit of the circular buffer prior to the writepointer and ending at a dirty region end bit of the circular buffersubsequent to the write pointer. The read module is coupled with thedirty region processor to set a read pointer location for a consumersystem as a location in the circular buffer outside the dirty region,and to initiate reading of data of the data stream at the read pointerlocation by the consumer system. In various embodiments, the system caninclude one or more producer systems, memory systems, and/or consumersystems.

This summary is not intended to identify key or essential features ofthe claimed subject matter, nor is it intended to be used in isolationto determine the scope of the claimed subject matter. The subject mattershould be understood by reference to appropriate portions of the entirespecification of this patent, any or all drawings, and each claim.

The foregoing, together with other features and embodiments, will becomemore apparent upon referring to the following specification, claims, andaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is described in conjunction with the appendedfigures:

FIG. 1 shows a shared audiovisual (A/V) production and consumptionenvironment, according to various embodiments;

FIG. 2 shows a representation of a shared access environment with anillustrative circular buffer;

FIG. 3 shows a portion of a shared access environment that includes aconsumer system with archival recording types of A/V targets;

FIG. 4 shows a portion of a shared access environment that includes aconsumer system with real-time recording types of A/V targets;

FIG. 5 shows another shared A/V production and consumption environment,according to various embodiments;

FIGS. 6A and 6B provide schematic illustrations of embodiments ofcomputer systems that can implement various system components and/orperform various steps of methods provided by various embodiments; and

FIG. 7 shows a flow diagram of an illustrative method for lock-freesharing of a circular buffer, according to various embodiments.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a second label(e.g., a lower-case letter) that distinguishes among the similarcomponents. If only the first reference label is used in thespecification, the description is applicable to any one of the similarcomponents having the same first reference label irrespective of thesecond reference label.

DETAILED DESCRIPTION

Embodiments of the disclosed technology will become clearer whenreviewed in connection with the description of the figures herein below.In the following description, numerous specific details are set forth toprovide a thorough understanding of the present invention. However, onehaving ordinary skill in the art should recognize that the invention maybe practiced without these specific details. In some instances,circuits, structures, and techniques have not been shown in detail toavoid obscuring the present invention.

Turning to FIG. 1, a shared audiovisual (A/V) production and consumptionenvironment 100 is shown, according to various embodiments. Theenvironment 100 includes an A/V source 105, a producer system 110, amemory system 130, and one or more consumer systems 150. The variouscomponents are illustrated as coupled with each other. Such coupling canbe implemented in any suitable manner. In some implementations, all ofthe A/V source 105, the producer system 110, the memory system 130, andone or more consumer systems 150 are integrated into a single lock-freecircular buffer sharing system. In other embodiments, the lock-freecircular buffer sharing system includes only a portion of the componentsillustrated in FIG. 1. In some embodiments, each of the A/V source 105,the producer system 110, the memory system 130, and one or more consumersystems 150 are implemented as separate systems, coupled together by anysuitable wired and/or wireless connections. In one such embodiment, theA/V source 105 is connected with the producer system 110 via a wiredconnection (e.g., hard-wired, coupled via a standard or dedicatedphysical port, etc.); and the producer system 110 and one or moreconsumer systems 150 are in communication with the memory system 130 viaa high-bandwidth wireless network. In another such embodiment, the A/Vsource 105, the producer system 110, and the memory system 130 are allintegrated into a single system (e.g., a security camera with anintegrated buffer); and the one or more consumer systems 150 are incommunication with the integrated system via wired and/or wirelessconnections. In embodiments in which one or more components is coupledvia a network, the network (not shown) can include any suitable wiredand/or wireless communication links, such as long-range wired and/orwireless links (e.g., cellular network links, cable network links,fiber-optic network links, satellite network links, etc.), medium-rangewireless links (e.g., wireless-fidelity (WiFi) network links, wirelesslocal area network (WLAN) links, etc.), short-range wireless links(e.g., Bluetooth network links, ZigBee network links, etc.), short-rangewired links (e.g., coaxial links, high-definition multimedia interface(HDMI) links, etc.), etc.

For the sake of illustration, the environment 100 can be a securitycamera environment. In such an environment 100, the A/V source 105includes a security camera that can receive A/V information, includingvideo information (e.g., and audio information, in some cases). Thefootage is captured by the producer system 110 and converted into an A/Vdata stream, which is written to a shared circular buffer 135 of thememory system 130. While the data stream is being written, the one ormore consumer systems 150 can read data from the circular buffer 135.Only one A/V data stream write path is shown for the sake of simplicity.However, in some such environments, A/V data from multiple A/V sources105 (e.g., multiple security cameras directed at multiple locations) canbe written to multiple respective circular buffers 135 of one or morememory systems 130 by one or more producer systems 110; and some or allof multiple consumer systems 150 can read from the multiple circularbuffers 135 in a shared manner.

In the past, applications involving recording of continuously acquireddata streams (e.g., as from security cameras, certain sensors, etc.)involved recording directly to a storage medium (e.g., a magnetic tape)with limited capacity and changing to a different storage medium (e.g.,by inserting a new magnetic tape) to continue recording. More recently,such applications began using buffers, including circular buffers, toprovide a more continuous recording experience. A circular buffer is atype of memory that effectively has no beginning or end, so thatearlier-recorded data can continuously and sequentially be overwrittenby newly recorded data (e.g., the newest data continuously overwritesthe oldest data in the buffer). As such, circular buffers can enablecontinuous recording, even with limited storage capacity. For example,in context of a security camera, the camera can continuously recordwithout concern that it will reach the end of the buffer memory.

However, problems can arise when providing read access during suchcontinuous recording, particular when providing read access concurrentlyto multiple systems. For example, ensuring that systems are readingstable data can involve ensuring that such data is not being accessed byother systems at the same time. To that end, conventionally, when aparticular system desires to read from the circular buffer, theparticular system requests a buffer lock. For example, the buffer lockhalts any new writing to the buffer and restricts all reading only tothe particular system to help ensure that the particular system can readfrom a stable environment. While this can be an effective approach insome cases for a single reading system (and even, in some cases, for asmall number of reading systems), the approach can have limitations,including not scaling well to larger numbers of reading systems. Forexample, during the time each reading system locks the buffer, new datais not being recorded. As the number of reading systems increases, theamount of time the buffer is locked similarly increases. At some point,the multiple buffer locks cause no new writing to occur for anundesirably long period of time. Similarly, at times, a reading systemmay fail to release its buffer lock (e.g., though it has completedreading, it fails to unlock the buffer). In such cases, the entiresystem can effectively fail, as no new data is written to the system.

Embodiments described herein seek to provide access to shared circularbuffer resources without relying on buffer locks. For example, evenwhile the producer system 110 continues to write to the circular buffer135 of the memory system 130, embodiments can provide shared read accessto one or more consumer systems 150. According to such embodiments, oneor more consumer systems 150 can access live data being written to thecircular buffer 135 by the producer system 110 without managing bufferlocks, without waiting for other systems to release buffer locks, andwithout concern that another system will fail to release a buffer lock.

Embodiments can operate in any suitable context. For example, whiledescribed above in context of a security camera, the A/V source 105 caninclude any suitable type of sensor. In some implementations, the A/Vsource 105 includes a video camera, or other video sensors. In someimplementations, the A/V source 105 includes a microphone, or otheraudio transducer, or audio sensors. In some implementations, the A/Vsource 105 includes environmental sensors, such as temperature sensors,pressure sensors, light sensors, accelerometers, gyroscopic sensors,etc. Further, while described herein as “audiovisual” data, or “A/V”data, the data (and data streams) can include any suitable datacorresponding to the type of A/V source 105. For example, an A/V source105 that includes a camera can obtain data that includes video data,while an A/V source 105 that includes a gyroscopic sensor can obtaindata that includes gyroscopic data. Similarly, components of theproducer system 110, the memory system 130, the consumer system(s) 150,etc. can be configured in accordance with the type of A/V source 105 andcorresponding type of data being obtained. For example, inimplementations having an A/V source 105 that includes a high-definitionvideo camera, it may be desirable for the producer system 110 to includehigh-bitrate components and for the memory system 130 to allocate largercapacity to the circular buffer 135. In contrast, in implementationshaving an A/V source 105 that includes a narrow-band Internet of Things(nb-IoT) temperature sensor, it may be possible to implement theproducer system 110 with low-bitrate components and to implement thememory system 130 with a smaller-capacity circular buffer 135.

Embodiments of the producer system 110 include a capture module 115 anda write module 120. The capture module 115 is coupled with the A/Vsource 105 to capture data obtained by the A/V source 105 and togenerate a data stream from the data. Generation of the data stream caninvolve any suitable processing, such as amplifying, filtering,transcoding, encoding, packetizing, modulating, etc. The write module120 is coupled with the capture module 115 and the circular buffer 135to receive the data stream and to write the data stream to the circularbuffer 135. The write module 120 can write the data stream to thecircular buffer 135 in any suitable manner, for example, in any suitableformat and at any suitable bitrate or bitrates.

When the write module 120 begins to write the data stream to thecircular buffer 135, the write module 120 can also recordcharacteristics of the writing to a shared metadata 140 file. Asdescribed herein, the shared metadata 140 is used to enable shared,lock-free read access to the circular buffer 135 by the one or moreconsumer systems 150. In some embodiments, the shared metadata 140indicates a start time at which the write module 120 began writing thedata stream that is currently being written to the circular buffer 135.The start time can be recorded with reference to any suitable clockand/or buffer reference. For example, the start time can be recorded inmilliseconds, and it can be assumed that the write module 120 alwaysbegins to write at an address ‘0’. In other implementations, the writemodule 120 may begin writing a data stream at any buffer location (e.g.,where the previously written data stream ended), in whichimplementations the start time can indicate both a time and a bufferlocation where the current writing began. In some embodiments, theshared metadata 140 also indicates the bitrate at which the write module120 is currently writing. In other embodiments, the bitrate of the writemodule 120 can be obtained without referencing the shared metadata 140.For example, in implementations for which the write module 120 ishard-coded always to write at a single bitrate, other components mayknow the bitrate of the write module 120 without having to consult theshared metadata 140 (and the shared metadata 140 may not include suchdata, accordingly). The shared metadata 140 can include any othersuitable information in various embodiments. For example, it can bedesirable in certain applications for the shared metadata 140 toindicate an identification of the A/V source 105 (e.g., where theproducer system 110 is in communication with multiple A/V sources 105),an end time of a previously written data stream, an encoding format,etc. Some implementations of the shared metadata 140 also includeinformation about the circular buffer 135, such as buffer size. In someembodiments, as illustrated, the shared metadata 140 is stored in thememory system 130 along with the circular buffer 135. In otherembodiments, the shared metadata 140 is stored by the write module 120,or in any other suitable location that is accessible to other componentsto facilitate features described herein.

Embodiments of the circular buffer 135 can buffer the data stream usingany suitable type of memory, any suitable memory block size, etc. Thecircular buffer 135 can be implemented as a circular queue, a cyclicbuffer, a ring buffer, or any other end-to-end-connected data structureof fixed size. As described herein, the circular buffer 135 permitscontinuous writing of the data stream by the write module 120. Forexample, the oldest data in the circular buffer 135 is continuouslyoverwritten by the newest data being written to the circular buffer 135.

Embodiments of the consumer systems 150 include a write pointerprocessor 155, a dirty region processor 160, a read module 165, and anA/V target 170. The components of a particular consumer system 150 canbe integrated in a single package or distributed among multiplepackages. For example, the A/V target 170 can be a separate componentthat is coupled with other components of the consumer system 150 via awired or wireless connection. The write pointer processor 155 cancompute a write pointer location as a function of the start time and thebitrate of the data stream that is currently being written to thecircular buffer 135 by the producer system 110. For example, the writepointer processor 155 is coupled with the shared metadata 140 (e.g.,with the memory system 130) to obtain the start time (and the bitrate,in some cases). Embodiments of the write pointer processor 155 cancompute a present write pointer location by using the start time, thebitrate, the circular buffer 135 size, and a current time.

Embodiments of the dirty region processor 160 are coupled with the writepointer processor 155 to compute a dirty region around the write pointerlocation. The dirty region represent a region determined to be too closeto the write pointer location to permit a stable read environment. Forexample, it can be assumed that a consumer system 150 can safely readfrom anywhere in the circular buffer 135 outside of the dirty region.The dirty region is computed by the dirty region processor 160 to beginat a dirty region start bit of the circular buffer 135 prior to thewrite pointer and to end at a dirty region end bit of the circularbuffer 135 subsequent to the write pointer.

Having computed the dirty region, one or more consumer systems 150 canbe permitted to read from any location outside the dirty region. Theread modules 165 of each consumer system 150 can be coupled with thedirty region processor 160 to set a read pointer location for theconsumer system 150 as a location in the circular buffer 135 outside thedirty region. The read module 165 can then initiate reading of data ofthe data stream beginning at the read pointer location. As the data isread by the read module 165, the data can be passed to one or more A/Vtargets 170. The A/V targets 170 can include any suitable components bywhich to store and/or consume the data read from the circular buffer135. In some embodiments, the A/V target 170 includes local storage,such as a hard-disk drive, or other local archival storage. In otherembodiments, the A/V target 170 includes, or is in communication with,cloud storage, or other remote storage. In other embodiments, the A/Vtarget 170 includes a playback device, such as a video monitor, speaker,etc. In other embodiments, the A/V target 170 includes data processingand/or monitoring components, such as components to perform real-timeimage recognition, sensor data threshold detection, data aggregation,etc.

In some embodiments, the consumer system 150 can include a userinterface (UI) subsystem 175. The UI subsystem 175 can be used, forexample, to receive a request to read data from the circular buffer 135.The request can be received by a human user and/or from a machine user.For example, the UI subsystem 175 can include a graphical user interfacepresented via a display of the A/V target 170, virtual or physicalinterface controls integrated directly with the read module 165, etc. Insome embodiments, the computation of the write pointer location anddirty region are performed by the write pointer processor 155 and thedirty region processor 160 responsive to the request received via the UIsubsystem 175. For example, the write pointer location and dirty regionare computed with respect to a request time indicated by the receivedrequest (e.g., either the actual time of the request, or the requestindicates a subsequent read time).

In some embodiments, the producer system 110 includes a read director125. The read director 125 can signal the consumer systems 150 and/orotherwise direct operations thereof. In some embodiments, the readdirector 125 signals the consumer systems 150 when there is an update tothe shared metadata 140. For example, each time the producer system 110begins writing a new data stream, changes the bitrate at which it iswriting, etc., the read director 125 broadcasts a signal to all theconsumer systems 150. In some implementations, such a signal directs theconsumer systems 150 to consult the shared metadata 140 for updatedinformation. In other implementations, such a signal informs theconsumer systems 150 that any shared metadata 140 they previouslyobtained is now stale; as such, the next time the consumer systems 150desire to read from the circular buffer 135, the consumer systems 150know to re-acquire shared metadata 140 with updated information. Theread director 125 can use any suitable type of signaling. In oneimplementation, an inter-process communication (IPC) and/or remoteprocedure calling (RPC) protocol is used for signaling, such as thedesktop bus (D-BUS) protocol.

For the sake of illustration, FIG. 2 shows a representation of a sharedaccess environment 200 with an illustrative circular buffer 135. Thecircular buffer 135 includes a large number of data blocks arrangedsequentially according to arrow 230, and the data blocks are logicallyconnected end to end (i.e., a last memory address in the circular buffer135 is followed sequentially by a first address in the circular buffer135). The illustrated environment 200 shows a current write pointerlocation 310 at which a producer system 110 is presently writing a datastream. A dirty region 240 is defined around the write pointer location210 as a region between a dirty region start bit 242 of the circularbuffer 135 prior to the write pointer 210 and a dirty region end bit 244of the circular buffer 135 subsequent to the write pointer 210. Theillustrated environment 200 also shows different respective current readpointer locations 220 of four consumer systems 150.

As one illustrative example, the write pointer processor 155 computes apresent write pointer location of write pointer 210 by using the starttime, the bitrate, the circular buffer 135 size, and a current time.Suppose the circular buffer 135 size is 10 Megabytes(10*1024*1024=10,485,760 bytes). The shared metadata 140 indicates astart time of 1000 milliseconds and a bitrate of 8 megabits per second(Mbps) (1*1024*1024=1,048,576 bytes per second). One of the consumersystems 150 desires to access the data stream at 25,000 milliseconds.The write pointer processor 155 can compute that the elapsed writingtime for the current data stream is the time at which the consumersystem 150 desires access less the start time, or 25000−1000=24,000milliseconds. The total amount of data written during the elapsedwriting time can be computed as the bitrate (in bytes per millisecond)times the elapsed writing time, or 1048576/1000* 24000=25,165,824 bytes.The current write pointer offset address can be calculated as theremainder of the total amount of data written divided by the circularbuffer 135 size, or 25165824% 10485760=4,194,304 bytes, where ‘%’indicates a modulo operation. For example, if the write module 120 beganwriting the current data stream at address ‘0’ of the circular buffer135, the current write pointer location would be at the addresscorresponding to byte 4,194,304; if the write module 120 began writingthe current data stream at an address corresponding to byte 100,000 ofthe circular buffer 135, the current write pointer location would be atthe address corresponding to byte 4,294,304; and if the write module 120began writing the current data stream at an address corresponding tobyte 10,000,000 of the circular buffer 135, the current write pointerlocation would be at the address corresponding to byte 3,708,544 (i.e.,after wrapping around the circular buffer 135).

Having computed the location of the write pointer 210 (with the“current” location representing the location at the desired read time)by the write pointer processor 155, the dirty region processor 160 cancompute the dirty region 240. Extending the above example, suppose it isdesired to compute the dirty region 240 as a one-second region centeredaround the write pointer location 210. The dirty region processor 160can compute the dirty region start bit 242 as the current write pointeroffset location minus a half-second temporal distance, or4194304−(1048576/2)=3,670,016; bytes; and the dirty region processor 160can compute the dirty region end bit 244 as the current write pointeroffset location plus the half-second temporal distance, or4194304+(1048576/2)=4,718,592 bytes. In some embodiments, the dirtyregion 240 is computed to be symmetrical, such that the dirty regionstart bit 242 and the dirty region end bit 244 are approximately thesame distance (in opposite directions) from the write pointer 210. Inother embodiments, the dirty region 240 is computed to be asymmetrical,such that the dirty region start bit 242 is a first distance prior tothe write pointer 210, and the dirty region end bit 244 is a second,different distance subsequent to the write pointer 210. In someembodiments, the dirty region 240 is computed according to apredetermined value, such as a predetermined number of milliseconds ornumber of bytes. For example, the predetermined value can be based on apredetermined worst case read start lag time for a consumer system 150(e.g., a worst-case amount of time between when the consumer system 150assigns the read pointer 220 to a particular location and the consumersystem 150 begins actually reading from that location). In otherembodiments, the consumer system 150 has a read start lag time known toat least the consumer system 150. In some such embodiments, the dirtyregion 240 can be specifically computed for that consumer system 150 inaccordance with the particular read start lag time of that consumersystem 150.

While consumer systems 150 can safely read from any region of thecircular buffer 135 outside the dirty region 240, it can be desirable toset the respective read pointer 220 locations in accordance withadditional information in some cases. For example, different types ofA/V targets 170 can be more compatible with particular read pointer 220locations. For the sake of illustration, FIGS. 3 and 4 show twocategories of A/V targets 170 compatible with different read pointer 220locations.

FIG. 3 shows a portion of a shared access environment 300 that includesa consumer system 150 with archival recording types of A/V targets 170.The environment 300 can be a portion of environment 100 of FIG. 1 above,or of environment 500 of FIG. 5 below. As illustrated, the consumersystem 150 is in communication with a memory system 130, so that theread module 165 of the consumer system 150 can read from the circularbuffer 135 (not shown). The A/V target 170 of the consumer system 150includes both local and remote archival recording. For example, thelocal archival recording can include writing the data from the circularbuffer 135 to a non-transient storage medium (illustrated as hard-diskdrive 320), and the remote archival recording can include writing thedata form the circular buffer 135 to network storage (illustrated ascloud storage 310). In some such embodiments, it can be desirable tobegin reading from as far in the past as practical. Because, in thecircular buffer 135, the oldest data is continuously being overwrittenby the newest data, the oldest reliable data in the circular buffer 135can be considered the data just subsequent to the dirty region 240. Readpointer 220 a of FIG. 2 illustrates such a case, in which the locationof the read pointer 220 a is just after the end of the dirty region 240(i.e., at, or immediately subsequent to, the dirty region end bit 244).

FIG. 4 shows a portion of a shared access environment 400 that includesa consumer system 150 with real-time recording types of A/V targets 170.The environment 400 can be a portion of environment 100 of FIG. 1 above,or of environment 500 of FIG. 5 below. As illustrated, the consumersystem 150 is in communication with a memory system 130, so that theread module 165 of the consumer system 150 can read from the circularbuffer 135 (not shown). The A/V target 170 of the consumer system 150includes a real-time encoder 410 coupled with a display 420. Forexample, substantially as data is being read from the circular buffer135, the data is being encoded (e.g., and/or otherwise processed) foroutput by the encoder 410, and output to the display 420 for real-timeviewing. In another such embodiment, the encoder 410 can be configuredto perform other functions, such as real-time processing and analysis(e.g., for condition detection), and the display 420 can output resultsof the real-time processing and analysis, as appropriate. In some suchembodiments, it is desirable to begin reading from as close to thepresent as practical. Because the write pointer 210 is where the newestdata is being written to the circular buffer 135, the newest reliabledata in the circular buffer 135 can be considered the data just prior tothe dirty region 240. Read pointer 220 b of FIG. 2 illustrates such acase, in which the location of the read pointer 220 b is just prior tothe start of the dirty region 240 (i.e., at, or immediately prior to,the dirty region start bit 242).

Various modifications can be made to embodiments described above. Forexample, FIG. 5 shows a shared A/V production and consumptionenvironment 500 different from the environment 100 of FIG. 1, accordingto various embodiments. As in FIG. 1, the environment 500 in FIG. 5includes an A/V source 105, a producer system 110, a memory system 130,and one or more consumer systems 150. Also as in FIG. 1, the producersystem 110 includes a capture module 115, a write module 120, and a readdirector 125; the memory system 130 includes a shared circular buffer135 and shared metadata 140; and the consumer systems 150 include readmodules 165 and A/V targets 170.

Unlike in FIG. 1, the write pointer processor 155 and the dirty regionprocessor 160 in FIG. 5 are implemented in the read director 125 of theproducer system 110. In such embodiments, the producer system 110 cantrack its own shared metadata 140 and can use the shared metadata 140 toinform a requesting consumer system 150 of an appropriate read pointerlocation (or of the dirty region, as an indication of inappropriate readpointer locations). In some embodiments, when a consumer system 150 ispreparing to read from the circular buffer 135, the consumer system 150queries the read director 125 with a read request time (e.g., indicatinga time at which the consumer system 150 desires to start reading). Inresponse to the query, the read director 125 uses the write pointerprocessor 155 to compute a write pointer location at the read requesttime (e.g., where the write pointer will be at the requested read starttime), and uses the dirty region processor 160 to compute a dirty regionat the read request time. In response to the query, the read director125 can return information to the read module 165 from which the readmodule 165 can determine an appropriate read pointer location.

Embodiments of the producer system 110, the consumer systems 150, and orcomponents thereof, can be implemented on, and/or can incorporate, oneor more computer systems, as illustrated in FIGS. 6A and 6B. FIGS. 6Aand 6B provide schematic illustrations of embodiments of computersystems 600 that can implement various system components and/or performvarious steps of methods provided by various embodiments. It should benoted that FIG. 6 is meant only to provide a generalized illustration ofvarious components, any or all of which may be utilized as appropriate.FIG. 6, therefore, broadly illustrates how individual system elementsmay be implemented in a relatively separated or relatively moreintegrated manner.

The computer system 600 is shown including hardware elements that can beelectrically coupled via a bus 605 (or may otherwise be incommunication, as appropriate). The hardware elements may include one ormore processors 610, including, without limitation, one or moregeneral-purpose processors and/or one or more special-purpose processors(such as digital signal processing chips, graphics accelerationprocessors, video decoders, and/or the like); one or more input devices615, which can include, without limitation, a mouse, a keyboard, remotecontrol, and/or the like; and one or more output devices 620, which caninclude, without limitation, a display device, a printer, and/or thelike. In some implementations, the computer system 600 is a servercomputer configured to interface with additional computers (not withhuman users), such that the input devices 615 and/or output devices 620include various physical and/or logical interfaces (e.g., ports, etc.)to facilitate computer-to-computer interaction and control.

The computer system 600 may further include (and/or be in communicationwith) one or more non-transitory storage devices 625, which cancomprise, without limitation, local and/or network accessible storage,and/or can include, without limitation, a disk drive, a drive array, anoptical storage device, a solid-state storage device, such as a randomaccess memory (“RAM”), and/or a read-only memory (“ROM”), which can beprogrammable, flash-updateable and/or the like. Such storage devices maybe configured to implement any appropriate data stores, including,without limitation, various file systems, database structures, and/orthe like.

The computer system 600 can also include a communications subsystem 630,which can include, without limitation, a modem, a network card (wirelessor wired), an infrared communication device, a wireless communicationdevice, and/or a chipset (such as a Bluetooth™ device, an 802.11 device,a WiFi device, a WiMax device, cellular communication device, etc.),and/or the like. The communications subsystem 630 may permit data to beexchanged with a network, other computer systems, and/or any otherdevices described herein.

In many embodiments, the computer system 600 will further include aworking memory 635, which can include a RAM or ROM device, as describedherein. The computer system 600 also can include software elements,shown as currently being located within the working memory 635,including an operating system 640, device drivers, executable libraries,and/or other code, such as one or more application programs 645, whichmay include computer programs provided by various embodiments, and/ormay be designed to implement methods, and/or configure systems, providedby other embodiments, as described herein. Merely by way of example, oneor more procedures described with respect to the method(s) discussedherein can be implemented as code and/or instructions executable by acomputer (and/or a processor within a computer); in an aspect, then,such code and/or instructions can be used to configure and/or adapt ageneral purpose computer (or other device) to perform one or moreoperations in accordance with the described methods.

For example, turning to FIG. 6A, the computer system 600 a is shown asimplementing an illustrative consumer system 150. The computer system600 a can be in communication with the memory system 130 (e.g., with thecircular buffer 135 and/or the shared metadata 140) via thecommunications subsystem 630 (e.g., directly, via a network, etc.). Theworking memory 635 can be used to implement embodiments of the writepointer processor 155, the dirty region processor 160, and/or the readmodule 165. For example, each such component can be implemented asinstructions, which, when executed, cause the processor(s) 610 toperform functions of those components. The read module 165 can outputdata to the A/V target 170 in any suitable manner. In oneimplementation, data is communicated to the A/V target 170 via thecommunications subsystem 630. In another implementation, the A/V target170 is an output device 620 of the computer system 600 a. In someembodiments, the computer system 600 a can also receive varioussignaling, such as by the read director 125 (via the communicationssubsystem 630) and/or from the UI subsystem, which can be implementedusing input devices 615 of the computer system 600 a.

Turning to FIG. 6B, the computer system 600 b is shown as implementingan illustrative producer system 110. The computer system 600 b can be incommunication with the memory system 130 (e.g., with the circular buffer135 and/or the shared metadata 140) via the communications subsystem 630(e.g., directly, via a network, etc.) and/or the memory system 130 canbe implemented in the storage devices 625 of the computer system 600 b.The working memory 635 can be used to implement embodiments of thecapture module 115, the write module 120, and/or the read director 125.For example, each such component can be implemented as instructions,which, when executed, cause the processor(s) 610 to perform functions ofthose components. The capture module 115 can obtain data from the A/Vsource 105 in any suitable manner. In one implementation, data isobtained from the A/V source 105 via the communications subsystem 630.In another implementation, the A/V source 105 is an input device 615 ofthe computer system 600 b. In some embodiments, the computer system 600b can also communicate with the consumer systems 150 (via thecommunications subsystem 630), such as by broadcasting signaling data.

A set of these instructions and/or codes can be stored on anon-transitory computer-readable storage medium, such as thenon-transitory storage device(s) 625 described above. In some cases, thestorage medium can be incorporated within a computer system, such ascomputer system 600. In other embodiments, the storage medium can beseparate from a computer system (e.g., a removable medium, such as acompact disc), and/or provided in an installation package, such that thestorage medium can be used to program, configure, and/or adapt a generalpurpose computer with the instructions/code stored thereon. Theseinstructions can take the form of executable code, which is executableby the computer system 600 and/or can take the form of source and/orinstallable code, which, upon compilation and/or installation on thecomputer system 600 (e.g., using any of a variety of generally availablecompilers, installation programs, compression/decompression utilities,etc.), then takes the form of executable code.

It will be apparent to those skilled in the art that substantialvariations may be made in accordance with specific requirements. Forexample, customized hardware can also be used, and/or particularelements can be implemented in hardware, software (including portablesoftware, such as applets, etc.), or both. Further, connection to othercomputing devices, such as network input/output devices, may beemployed.

As mentioned above, in one aspect, some embodiments may employ acomputer system (such as the computer system 600) to perform methods inaccordance with various embodiments of the invention. According to a setof embodiments, some or all of the procedures of such methods areperformed by the computer system 600 in response to processor 610executing one or more sequences of one or more instructions (which canbe incorporated into the operating system 640 and/or other code, such asan application program 645) contained in the working memory 635. Suchinstructions may be read into the working memory 635 from anothercomputer-readable medium, such as one or more of the non-transitorystorage device(s) 625. Merely by way of example, execution of thesequences of instructions contained in the working memory 635 can causethe processor(s) 610 to perform one or more procedures of the methodsdescribed herein.

The terms “machine-readable medium,” “computer-readable storage medium”and “computer-readable medium,” as used herein, refer to any medium thatparticipates in providing data that causes a machine to operate in aspecific fashion. These mediums may be non-transitory. In an embodimentimplemented using the computer system 600, various computer-readablemedia can be involved in providing instructions/code to processor(s) 610for execution and/or can be used to store and/or carry suchinstructions/code. In many implementations, a computer-readable mediumis a physical and/or tangible storage medium. Such a medium may take theform of a non-volatile media or volatile media. Non-volatile mediainclude, for example, optical and/or magnetic disks, such as thenon-transitory storage device(s) 625. Volatile media include, withoutlimitation, dynamic memory, such as the working memory 635.

Common forms of physical and/or tangible computer-readable mediainclude, for example, a floppy disk, a flexible disk, hard disk,magnetic tape, or any other magnetic medium, a CD-ROM, any other opticalmedium, any other physical medium with patterns of marks, a RAM, a PROM,EPROM, a FLASH-EPROM, any other memory chip or cartridge, or any othermedium from which a computer can read instructions and/or code.

Various forms of computer-readable media may be involved in carrying oneor more sequences of one or more instructions to the processor(s) 610for execution. Merely by way of example, the instructions may initiallybe carried on a magnetic disk and/or optical disc of a remote computer.A remote computer can load the instructions into its dynamic memory andsend the instructions as signals over a transmission medium to bereceived and/or executed by the computer system 600.

The communications subsystem 630 (and/or components thereof) generallywill receive signals, and the bus 605 then can carry the signals (and/orthe data, instructions, etc., carried by the signals) to the workingmemory 635, from which the processor(s) 610 retrieves and executes theinstructions. The instructions received by the working memory 635 mayoptionally be stored on a non-transitory storage device 625 eitherbefore or after execution by the processor(s) 610.

It should further be understood that the components of computer system600 can be distributed across a network. For example, some processingmay be performed in one location using a first processor while otherprocessing may be performed by another processor remote from the firstprocessor. Other components of computer system 600 may be similarlydistributed. As such, computer system 600 may be interpreted as adistributed computing system that performs processing in multiplelocations. In some instances, computer system 600 may be interpreted asa single computing device, such as a distinct laptop, desktop computer,or the like, depending on the context.

Systems including those described above can be used to implement variousmethods. FIG. 7 shows a flow diagram of an illustrative method 700 forlock-free sharing of a circular buffer, according to variousembodiments. Embodiments of the method 700 can begin at stage 704 byreceiving a request to read data from a circular buffer having a datastream being written thereto by a producer system at a bitrate. Therequest can be received by a consumer system at a request time. At stage708, embodiments can consult shared metadata indicating a start time ofthe data stream. In some embodiments, the shared metadata indicatesadditional information, such as a bitrate of the current data stream, astart offset location for the write pointer, etc. In some embodiments,the consulting at stage 708 is responsive to the receiving at stage 704.In other embodiments, the consulting at stage 708 is responsive toreceiving signaling from the producer system indicating an update to theshared metadata.

At stage 712, embodiments can compute a predicted write pointer locationcorresponding to the request time as a function of the start time andthe bitrate of the data stream. At stage 716, embodiments can compute adirty region around the write pointer location. The dirty region can becomputed as beginning at a dirty region start bit of the circular bufferprior to the write pointer and as ending at a dirty region end bit ofthe circular buffer subsequent to the write pointer. In someembodiments, computing the dirty region at stage 716 includesdetermining a read start lag time for the consumer system and computinga bit-wise lag time as a number of bits of the circular buffercorresponding to the read start lag time as a function of the bitrate.In such embodiments, the dirty region start bit of the circular buffercan be computed as preceding the write pointer by at least the bit-wiselag time, and/or the dirty region end bit of the circular buffer can becomputed as subsequent to the write pointer by at least the bit-wise lagtime. In other embodiments, computing the dirty region at stage 716includes setting the dirty region start bit of the circular buffer priorto precede the write pointer by at least a number of bits correspondingto a predetermined real-time read start lag time, and/or setting thedirty region end bit of the circular buffer to follow the write pointerby at least a number of bits corresponding to a predetermined real-timeread start lag time.

At stage 720, embodiments can set a read pointer location for theconsumer system as a location in the circular buffer outside the dirtyregion. In some embodiments, the request is for real-time reading of thedata stream, and the read pointer location is set at stage 720 to a bitlocation of the circular buffer corresponding to the dirty region startbit (e.g., or immediately prior to the dirty region start bit). In otherembodiments, the request is for archival recording of the data stream,the read pointer location is set at stage 720 to a bit location of thecircular buffer corresponding to the dirty region end bit (e.g., orimmediately subsequent to the dirty region start bit). At stage 724,embodiments can initiate reading of data of the data stream at the readpointer location by the consumer system. The initiating can beresponsive to the request.

The methods, systems, and devices discussed above are examples. Variousconfigurations may omit, substitute, or add various procedures orcomponents as appropriate. For instance, in alternative configurations,the methods may be performed in an order different from that described,and/or various stages may be added, omitted, and/or combined. Also,features described with respect to certain configurations may becombined in various other configurations. Different aspects and elementsof the configurations may be combined in a similar manner. Also,technology evolves and, thus, many of the elements are examples and donot limit the scope of the disclosure or claims.

Specific details are given in the description to provide a thoroughunderstanding of example configurations (including implementations).However, configurations may be practiced without these specific details.For example, well-known circuits, processes, algorithms, structures, andtechniques have been shown without unnecessary detail in order to avoidobscuring the configurations. This description provides exampleconfigurations only, and does not limit the scope, applicability, orconfigurations of the claims. Rather, the preceding description of theconfigurations will provide those skilled in the art with an enablingdescription for implementing described techniques. Various changes maybe made in the function and arrangement of elements without departingfrom the spirit or scope of the disclosure.

Also, configurations may be described as a process which is depicted asa flow diagram or block diagram. Although each may describe theoperations as a sequential process, many of the operations can beperformed in parallel or concurrently. In addition, the order of theoperations may be rearranged. A process may have additional steps notincluded in the figure. Furthermore, examples of the methods may beimplemented by hardware, software, firmware, middleware, microcode,hardware description languages, or any combination thereof. Whenimplemented in software, firmware, middleware, or microcode, the programcode or code segments to perform the necessary tasks may be stored in anon-transitory computer-readable medium such as a storage medium.Processors may perform the described tasks.

Having described several example configurations, various modifications,alternative constructions, and equivalents may be used without departingfrom the spirit of the disclosure. For example, the above elements maybe components of a larger system, wherein other rules may takeprecedence over or otherwise modify the application of the invention.Also, a number of steps may be undertaken before, during, or after theabove elements are considered.

What is claimed is:
 1. A method for lock-free sharing of a circularbuffer, the method comprising: receiving, at a consumer system at arequest time, a request to read data from a circular buffer having adata stream being written thereto by a producer system at a bitrate;consulting shared metadata indicating a start time of the data stream;computing a predicted write pointer location corresponding to therequest time as a function of the start time and the bitrate of the datastream; computing a dirty region around the write pointer location, thedirty region beginning at a dirty region start bit of the circularbuffer prior to the write pointer and ending at a dirty region end bitof the circular buffer subsequent to the write pointer; setting a readpointer location for the consumer system as a location in the circularbuffer outside the dirty region; and initiating reading of data of thedata stream at the read pointer location by the consumer system, theinitiating being responsive to the request.
 2. The method of claim 1,wherein the shared metadata further indicates the bitrate, and thecomputing the predicted write pointer location is as a function of theshared metadata.
 3. The method of claim 1, wherein the consulting is bythe consumer system in response to the receiving the request.
 4. Themethod of claim 1, further comprising: receiving a signal from theproducer system indicating an update to the shared metadata, wherein theconsulting is by the consumer system in response to the receiving thesignal.
 5. The method of claim 4, wherein the signal indicates a newstart time and/or a new bitrate.
 6. The method of claim 1, wherein: therequest is for real-time reading of the data stream; and the setting theread pointer location is to a bit location of the circular buffercorresponding to the dirty region start bit.
 7. The method of claim 1,wherein: the request is for archival recording of the data stream; andthe setting the read pointer location is to a bit location of thecircular buffer corresponding to the dirty region end bit.
 8. The methodof claim 1, wherein the computing the dirty region comprises:determining a read start lag time for the consumer system; computing abit-wise lag time as a number of bits of the circular buffercorresponding to the read start lag time as a function of the bitrate;and computing at least one of: dirty region start bit of the circularbuffer as preceding the write pointer by at least the bit-wise lag time;or the dirty region end bit of the circular buffer as subsequent to thewrite pointer by at least the bit-wise lag time.
 9. The method of claim1, wherein the computing the dirty region comprises: setting the dirtyregion start bit of the circular buffer to precede the write pointer byat least a number of bits corresponding to a predetermined real-timeread start lag time.
 10. A lock-free circular buffer sharing systemcomprising: a write pointer processor to consult shared metadataindicating a start time of a data stream being written to a circularbuffer by a producer system at a bitrate, and to compute a write pointerlocation as a function of the start time and the bitrate of the datastream; a dirty region processor, coupled with the write pointerprocessor, to compute a dirty region around the write pointer location,the dirty region beginning at a dirty region start bit of the circularbuffer prior to the write pointer and ending at a dirty region end bitof the circular buffer subsequent to the write pointer; and a readmodule, coupled with the dirty region processor, to set a read pointerlocation for a consumer system as a location in the circular bufferoutside the dirty region, and to initiate reading of data of the datastream at the read pointer location by the consumer system.
 11. Thelock-free circular buffer sharing system of claim 10, furthercomprising: a memory system comprising the circular buffer and havingthe shared metadata stored therein.
 12. The lock-free circular buffersharing system of claim 10, further comprising: the consumer systemcomprising the write pointer processor, the dirty region processor, andthe read module.
 13. The lock-free circular buffer sharing system ofclaim 10, further comprising: the producer system comprising: a capturemodule to capture audiovisual data from an audiovisual source; and awrite module, coupled with the capture module and the circular buffer,to write the audio visual data as the data stream to the circular bufferand to write the shared metadata.
 14. The lock-free circular buffersharing system of claim 13, wherein the producer system furthercomprises: a read director comprising the write pointer processor andthe dirty region processor.
 15. The lock-free circular buffer sharingsystem of claim 10, wherein the read module is further to: receive arequest from a user interface to read the data from the circular buffer;and direct the write pointer processor to consult the shared metadataresponsive to the signal.
 16. The lock-free circular buffer sharingsystem of claim 10, wherein the read module is further to: receive asignal from the producer system indicating an update to the sharedmetadata; and direct the write pointer processor to consult the sharedmetadata responsive to the signal.
 17. The lock-free circular buffersharing system of claim 10, wherein: the consumer system is configuredfor real-time reading of the data stream; and the read module is to setthe read pointer location to a bit location of the circular bufferproximate to and preceding the dirty region start bit.
 18. The lock-freecircular buffer sharing system of claim 10, wherein: the consumer systemis configured for archival recording of the data stream; and the readmodule is to set the read pointer location to a bit location of thecircular buffer proximate to and subsequent to the dirty region end bit.19. The lock-free circular buffer sharing system of claim 10, whereinthe dirty region processor is to compute the dirty region by:determining a read start lag time for the consumer system; computing abit-wise lag time as a number of bits of the circular buffercorresponding to the read start lag time as a function of the bitrate;and computing at least one of: dirty region start bit of the circularbuffer prior as preceding the write pointer by at least the bit-wise lagtime; or the dirty region end bit of the circular buffer as subsequentto the write pointer by at least the bit-wise lag time.
 20. Thelock-free circular buffer sharing system of claim 10, wherein the dirtyregion processor is to compute the dirty region by setting the dirtyregion start bit of the circular buffer prior to precede the writepointer by at least a number of bits corresponding to a predeterminedreal-time read start lag time.